The present invention relates to a battery pack, and a battery charging system using the battery pack, and particularly relates to a protection apparatus for a rechargeable battery effective for a lithium ion rechargeable battery.
The following section describes, with reference to FIG. 4, conventional protection control for a battery pack including a lithium ion rechargeable battery as a power supply for portable electronic equipment. A lithium ion rechargeable battery 111 is serially connected between a positive terminal 116 and a negative terminal 117 through a reverse-current-preventing diode 115. Simultaneously, a FET switch 114 including a MOS FET with a parasitic diode for protecting against overcharge (referred to as a charge FET hereafter), and a MOS FET with a parasitic diode for protecting against overdischarge (referred to as a discharge FET hereafter), is serially connected with the rechargeable battery 111. A control circuit 112 for controlling the turning on and off of the charge FET, and the discharge FET, of the FET switch 114 is provided. A discharge current represented as a voltage on both sides of the lithium ion rechargeable battery 111, and a voltage on both sides of the FET switch 114, is supplied for the control circuit 112. This control circuit 112 uses the FET switch 114 to conduct four-value control including turning on both charge and discharge, turning on only charge, turning on only discharge, and turning off both charge and discharge through a flip-flop 113 based on the entered information. A protection circuit including the control circuit 112, the flip-flop 113, the FET switch 114, is generally referred to as an SU (Safety Unit).
Thus, when the portable electronic equipment is charged, two types of control including: the charge control by the main unit of the electronic equipment or a battery charger; and the control by the aforementioned SU in the battery pack which is activated if the charge control fails, exist independently for controlling the charge. The following section describes how these two types of control operate generally.
The charge control by the portable electronic equipment or the battery charger in a normal state can be any one of: (1) constant voltage charge at 4.2 V, (2) maximum current control at 0.7 C, and (3) charge completion control (based on the current, the charge period, or combination thereof), and the SU in the battery pack does not operate. When these types of charge control are not operable, such as due to a failure or a malfunction, the SU in the battery pack controls to (1) disconnect a charge circuit (the disconnection may be recoverable or non-recoverable) when a voltage of 4.35 Vxc2x10.05 V is detected, which is a range set so as not to overlap the normal fluctuation range of the charge voltage in consideration of temperature variation and tolerance from the control of the charge voltage; and to (2) disconnect the charge circuit when the maximum current of 2.0 C to 4.0 C is detected. Further, in the case that the SU does not operate, the portable electronic equipment or the battery charger provide such protection functions as: (1) disconnecting the charge circuit when the voltage of 4.55 Vxc2x10.05 V is detected, (2) disconnecting the charge circuit when a current of 1.3 times of the maximum charge current is detected, (3) not charging when the surface temperature of the lithium ion rechargeable battery 111, which is detected by a thermistor 119 and is transmitted through a battery-pack-side temperature detection terminal 118, is out of the range of 0xc2x0 C. to 40xc2x0 C., and (4) stopping the charge after a timer count up two to three hours.
In this manner, the reliability (safety) of the product is secured while there are provided multiple methods of protection for charging the lithium ion rechargeable battery in case of a failure as a basic policy.
However, since the multiple methods of protection are provided for the above-mentioned conventional battery pack with an integrated SU and the conventional battery charging system using this type of the battery pack while it is assumed that the SU exists in the battery pack, it is apparently impossible to eliminate the SU. For the battery pack, the major parts of the SU alone, such as the control circuit 112, the flip-flop 113, and the FET switch 114, account for about 30% of the total cost. This partially causes an increase in the cost of any such battery pack which includes the lithium ion rechargeable battery. Although all types of ideas such as one disclosed in Japanese Patent Laid-Open Publication No. Hei. 8-116627 are embodied for improving the protection features for an independent battery pack, applying all of them also cause a serious problem in terms of the cost.
An object of the present invention is to solve these conventional problems by improving an independent battery pack which includes a lithium rechargeable battery as a unit cell, especially a lithium ion rechargeable battery, as well as redesigning the entire battery charging system, thereby eliminating the principal parts of the SU while maintaining the multiple protection, with a resultant decrease in the cost largely, and while also reducing the development period and the size of the battery pack.
To achieve the object above, the battery charging system of the present invention includes a battery charging apparatus and a battery pack. The battery charging apparatus includes an AC/DC converter for converting commercial power supply to DC, a charge output terminal for supplying the battery pack with an output from the AC/DC converter, a GND terminal corresponding to the charge output terminal, voltage/current detection means provided on a charge path, over voltage protection means provided on the charge path, a voltage detection terminal for detecting a voltage of the battery pack, a temperature detection terminal for detecting a temperature of the battery pack, charge control means for conducting different types of charge control based on signals received from the voltage/current detection means, the voltage detection terminal, and the temperature detection terminal, and an output control switch which is provided on the charge path and conducts output control based on a signal received from the charge control means. The battery pack includes a lithium ion rechargeable battery to be charged, a positive terminal and a negative terminal for electrically connecting the lithium ion rechargeable battery with the battery charging apparatus, a thermistor for detecting a surface temperature of the rechargeable battery, and a battery-pack-side temperature detection terminal for providing the battery charging apparatus with temperature information detected by the thermistor. The battery charging system of the present invention conducts protection control for the battery pack such that the charge control means transmits a signal to the output control switch for turning off an output when a rise rate of the battery pack temperature received by the charge control means through the battery-pack-side temperature detection terminal and the temperature detection terminal is equal to or more than a predetermined value.
With this constitution, it is preferable that the lithium ion rechargeable battery used as a unit cell includes an overcharge-inhibition additive. With this additive, since the battery surface temperature rises early or rapidly when overcharge occurs, the protection control activated by the rise in the temperature is executed earlier or more easily.
In addition to the battery charging apparatus, the battery charging system of the present invention includes a battery pack including a lithium ion rechargeable battery to be charged, a positive terminal and a negative terminal for electrically connecting the lithium ion rechargeable battery with the battery charging apparatus, battery voltage detection means for detecting the battery voltage of the lithium ion rechargeable battery, and a battery-pack-side voltage detection terminal for providing the battery charging apparatus with voltage information detected by the battery voltage detection means. When a rise rate of the battery pack voltage received by the charge control means through the battery-pack-side voltage detection terminal and the voltage detection terminal is equal to or less than a predetermined value, the battery charging system conducts protection control for the battery pack such that the charge control means transmits a signal for turning off the output to the output control switch.
With this constitution, it is preferable that the lithium ion rechargeable battery used as a unit cell includes an overcharge-inhibition additive. With this additive, since a change of the rise rate of the battery voltage occurs early when overcharge occurs, the protection control activated by the change of the rise in the voltage is executed earlier or more easily.
Consequently, it is possible to largely decrease the cost, and to reduce the size and the development period of the battery pack by eliminating the principal parts of the SU from the battery pack without adding specific constitution elements while the battery charging system as a whole is providing the multiple protection.